Fill down datetime based on date and time columns

Hi all,

I'm trying to fill down the datetime column based on date and time columns as you can see on the picture below.

Date column was extracted from the log column that consists Date everytime when the logging started and down below this Date column is another date, but between it is not recorded. The time column is filled 100% and never null. My problem is I cannot fill down the date based on time reading. Any suggestions how I can solve it? 

P.S.: Yes, I tried to configure logging so it will also include both date with time, but I was told this was not possible.

regards,

Nurbek